1. Field of Invention
The present invention relates to an electric-component mounting head which is employed in an electric-component mounting apparatus and particularly to the art of controlling a mounting load as a pressing load with which an electric component (e.g., an electronic component) is pressed against an object (e.g., a printed wiring board) when the electric component is mounted on the object.
2. Related Art Statement
FIG. 8 schematically shows a conventional electric-component ("EC") mounting head 100. The EC mounting head 100 includes (a) a support member 102, (b) a suction nozzle 104 which applies a suction to an EC and thereby holds the EC, (c) a ball spline 106 which connects the suction nozzle 104 to the support member 102 such that the nozzle 104 is movable relative to the support member 102 in a direction parallel to an axis line of the nozzle 104, and (d) a coil spring 108 which biases the suction nozzle 104 in a downward direction. The ball spline 106 includes a ball-spline axis member 110 fixed to the support member 102, and a ball-spline nut 112 fitted on the axis member 110 via balls. The suction nozzle 104 is held by the nut 112, and is biased by the coil spring 108 via the nut 112. The support member 102 is elevated and lowered by an elevating and lowing device (not shown).
Before the EC mounting head 100 starts an EC mounting operation, a relationship between the position of the suction nozzle 104 relative to the support member 102 and the downward force applied to the nozzle 104 is determined and, based on the thus determined relationship, a desired position to which the support member 102 is moved downward by the elevating and lowering device is determined. More specifically described, a contact sensor 114 detects a "contact" position of the support member 102 where the EC held by the suction nozzle 104 contacts an object (e.g., a printed wiring board, "PWB"), and a control device (not shown) controls, according to the determined relationship, an amount of downward movement (i.e., a downward stroke) of the support member 102 from the detected "contact" position, so that a desired downward force may be applied to the suction nozzle 104 and accordingly the EC held by the nozzle 104 may be mounted on the object with a desired mounting load. Thus, the conventional EC mounting head 100 essentially needs, for pressing an EC against an object with an appropriate load, the determination of a relationship between the position of the suction nozzle 104 relative to the support member 102 and the downward force applied to the nozzle 104, and an accurate control of downward stroke of the support member 102.
In addition, a minimal mounting load of the conventional EC mounting head 100 mainly depends on (1) the total weight of the suction nozzle 104 and one or more members which is or are moved as a unit with the nozzle 104, (2) an elastic force of the coil spring 108 when the support member is moved downward to, and stopped at, the desired position, and (3) a resistance to the relative movement between the ball-spline axis member 110 and the ball-spline nut 112. Thus, it has been difficult to sufficiently decrease the minimal mounting load.